1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same. More particularly, the present invention relates to a semiconductor device using shallow trench isolation.
2. Description of the Related Art
Highly integrated semiconductor devices often adopt shallow trench isolation. Isolation has been conventionally achieved by a LOCOS (Local Oxidation of Silicon) technique. However, the LOCOS technique has difficulties in fabricating highly integrated semiconductor devices, such as bird's beaks and poor isolation abilities. This situation encourages the adoption of the shallow trench isolation.
FIG. 1 shows a conventional structure of a semiconductor devices using shallow trench isolation. A trench 102 is formed on a silicon substrate 101. The inner surface of the trench 102 is coated by a silicon oxide film 103 formed by thermal oxidization. A liner 104 made of silicon nitride is formed on the silicon oxide film 103. A silicon oxide film 105 is formed on the liner 104 to fill the trench 102.
The liner 104 relaxes the interior stress induced in the silicon substrate 101. The shallow trench isolation causes the interior stress to be applied to the silicon substrate 101, because of the difference in thermal expansion coefficients between the silicon substrate 101 and the silicon oxide film 105. The stress applied to the silicon substrate 101 induces crystal defects in the silicon substrate, and thus increases junction leak currents. The increase in the junction leak currents causes improper operations of semiconductor devices. The relaxation of the internal stress by the liner 104 reduces the junction leak current and thus improves the reliability of the semiconductor device.
It is desired that the internal stress of the semiconductor substrate be further reduced. The reduction of the internal stress efficiently improves the reliability of the semiconductor device.